I wasn't aware of the print rule either, and came up with a somewhat convoluted solution which may be of help.

It's essentially just a bash script which generates the file in a destination made by mktemp, then compares the temporary file with the destination, and updates if necessary.

It has to be run in the Jamroot, not in a lower level Jamfile because jam globbing doesn't pick up the generated files in time if it's done in the Jamfile.

$ cat Jamroot

path-constant TOP : . ;

# generate current version information

# (done here because jam globbing doesn't pick up generated files on time if done in their respective jamfiles)

Echo [ SHELL "$(TOP)/common/version/generate.sh $(TOP) $(TOP)/common/version/bin_version.cc" ] ;

.....

$ cat common/version/generate.sh

#!/bin/bash

readonly TOP=$1; shift

readonly TEMP_DIR=$(mktemp -dt "$(basename $0.XXXXXXXXXX)")

trap "rm -rf ${TEMP_DIR}" EXIT

readonly VERSION=$(git describe --always --dirty --long --tags)

readonly NUM_COMMITS=$(git rev-list HEAD | wc -l | bc)

readonly BRANCH=$(git rev-parse --abbrev-ref HEAD)

readonly AHEAD_BY=$(git log --oneline origin/${BRANCH}..${BRANCH} | wc -l | bc)

readonly NUM_UNTRACKED=$(git ls-files --exclude-standard --others --full-name -- ${TOP} | wc -l | bc)

readonly HOSTNAME=$(hostname)

write_version_file()

{

local filename=${1}

cat <<- EOF > ${filename}

* Version information

* - This is a generated file - do not edit

#include "bin_version.h"

namespace app { namespace bin {

const char* version() { return "${VERSION}"; }

const char* num_commits() { return "${NUM_COMMITS}"; }

const char* date() { return __DATE__ " " __TIME__; }

const char* branch() { return "${BRANCH}"; }

const char* ahead_by() { return "${AHEAD_BY}"; }

const char* num_untracked() { return "${NUM_UNTRACKED}"; }

const char* user() { return "${USER}"; }

const char* hostname() { return "${HOSTNAME}"; }

}}

EOF

}

copy_if_different()

{

local src_file=$1

local dst_file=$2

if [ -f ${dst_file} ]; then

# diff the files

diff ${src_file} ${dst_file} > /dev/null

# if there are differences

if [ $? -ne 0 ]; then

echo "$(basename ${dst_file}) is out of date - updating"

mv ${src_file} ${dst_file}

else

echo "$(basename ${dst_file}) does not exist - creating"

mv ${src_file} ${dst_file}

}

main()

{

local dst_file=$1

local src_file=${TEMP_DIR}/version

write_version_file ${src_file}

copy_if_different ${src_file} ${dst_file}

printf "Version info: $VERSION\n"

printf "Num commits: $NUM_COMMITS"

}

main "$@"